Optical polarization

About: Optical polarization is a research topic. Over the lifetime, 13992 publications have been published within this topic receiving 244284 citations.

Synchronous optical and radio polarization variability in the Blazar OJ287

Abstract: We explore the variability and cross-frequency correlation of the flux density and polarization of the blazar OJ287, using imaging at 43 GHz with the Very Long Baseline Array, as well as optical and near-infrared (near-IR) polarimetry. The polarization and flux density in both the optical waveband and the 43 GHz compact core increased by a small amount in late 2005, and increased significantly along with the near-IR polarization and flux density over the course of 10 days in early 2006. Furthermore, the values of the electric vector position angle (EVPA) at the three wavebands are similar. At 43 GHz, the EVPA of the blazar core is perpendicular to the flow of the jet, while the EVPAs of emerging superluminal knots are aligned parallel to the jet axis. The core polarization is that expected if shear aligns the magnetic field at the boundary between flows of disparate velocities within the jet. Using variations in flux density, percentage polarization, and EVPA, we model the inner jet as a spine-sheath system. The model jet contains a turbulent spine of half-width 1fdg2 and maximum Lorentz factor of 16.5, a turbulent sheath with Lorentz factor of 5, and a boundary region of sheared field between the spine and sheath. Transverse shocks propagating along the fast, turbulent spine can explain the superluminal knots. The observed flux density and polarization variations are then compatible with changes in the direction of the inner jet caused by a temporary change in the position of the core if the spine contains wiggles owing to an instability. In addition, we can explain a stable offset of optical and near-IR percentage polarization by a steepening of spectral index with frequency, as supported by the data.

Optical polarization beam combiner/splitter

Abstract: An optical polarization beam splitter comprises a first optical fiber having an end defining a first optical axis, a second optical fiber having an end defining a second optical axis, and a third optical fiber having an end defining a third optical axis parallel to and spaced apart from the second optical axis. A collimating lens is disposed along the first optical axis positioned to form a collimated optical beam from the first optical fiber. A focussing lens is disposed along a path of the collimated optical beam. A birefringent walk-off crystal has a first face adjacent to the focussing lens and a second face located at a focal plane of the focussing lens and in contact with the ends of the second and third optical fibers. The birefringent crystal is oriented such that and has a thickness between its first and second faces selected such that a first component of the optical beam having a first polarization exits the crystal at its second face and enters the end of the second optical fiber along the second optical axis and a second component of the optical beam having a second polarization orthogonal to the polarization of the first polarization exits the crystal at its second face and enters the end of the third optical fiber along the third optical axis.

Optical variability of blazars

Abstract: Variability is one of the characteristics of blazars. The rapid variability is superposed on the long term variations. In this talk, the variability on different time scales, such as intra-day(IDV), short-term (STV), and long-term (LTV) variations are presented for some sources. For objects with many observations, we have made periodicity analysis, the results show that the long-term variation periodicity is in a range of about 1.4 to 18 years from our consideration. Some possible mechanisms for different time scales are also discussed. The optical polarization is correlated with the variation amplitude.

Iterative Polar Quantization-Based Modulation to Achieve Channel Capacity in Ultrahigh-Speed Optical Communication Systems

Abstract: In this paper, we propose a nonuniform coded-modulation format based on iterative polar quantization (IPQ) as a scheme to enable achieving channel capacity in ultrahigh-speed optical communication systems. The proposed modulation format is coded with structured low-density parity-check (LDPC) codes optimized for Gaussian channels and, in combination with polarization-multiplexing, can achieve 800 Gb/s per wavelength aggregate rate and beyond utilizing the currently available components operating at 50 GS/s. Using coded IPQ, we show that we can achieve capacity for signal-to-noise ratios (SNRs) of up to 25 dB and increase the total propagation distance over optical transmission systems by 275 km over coded star-quadrature amplitude modulation (QAM).

Polymorphism and penferroelectricity in PLZT ceramics

Abstract: The interaction of structure with optical and electrical properties in lanthanum-doped lead zirconate-titanate (PLZT) ceramics is complex. An interpretation is presented which shows the critical dependence of structure and, hence, properties on the state of polarization, the temperature, and the La content. To explain the behavior of PLZT ceramics two new concepts are presented: polymorphism and penferroelectricity. Polymorphism occurs when either electrical or mechanical ordering fields generate a hybrid crystal structure in which an individual grain attains a crystal structure dependent on its orientation with respect to the field. Penferro-electricity refers to the condition in which material is noncubic and polar but with such a low spontaneous polarization that no domains exist. The justification for applying these concepts to PLZT rests on the existing structural, optical, and dielectric data supplemented by new X-ray evidence and new data on the temperature dependence of optical and electrical properties. Emphasis is placed on materials with 65/35 Zr/Ti ratio and 6 < X ≤ 8 where X is the atom % La substituted for Pb. Analysis of existing data disclosed 1) a lack of X-ray evidence for the morphotropic boundary predicted by average remanent birefrigence and planar coupling and 2) a discrepancy in the position of the phase transition located by the Curie point and by planar coupling coefficient. The new X-ray, optical insertion loss, dielectric and piezo-electric data show conclusively that the phase equilibria in 65/35 PLZT depend strongly on the state of polarization. In thermally annealed ceramics a state of penferroelectricity exists between the cubic paraelectric state and the rhombohedral ferroelectric state. Rhombohedral ferroelectric material with 6 < X < 8 transforms to polymorphic material with very strong ferroelectric properties during poling. Because of the large crystal distortions which accompany poling, the optical transmission in the poled state is much reduced. This behavior is the basis for many of the useful device applications of PLZT in this compositional range.